Decorative shell



FIG. 1 is an isometric view of the decorative shell with the broken line showing for illustrative purposes only and forming no part of the claimed design;

FIG. 2 is a side elevational view of the decorative shell as depicted in FIG. 1, all four sides of the decorative shell being a mirror image thereof;

FIG. 3 is a plan view of the decorative shell as depicted in FIG. 1; and,

FIG. 4 is a bottom elevational view of the decorative shell as depicted in FIG. 1. 

The ornamental design for a decorative shell, as shown and described. 